A gas turbine engine effective for powering an aircraft at supersonic flight typically includes a variable area exhaust nozzle having primary and secondary exhaust flaps which are joined together to define a throat of minimum flow area with a converging channel defined by the primary flaps and a diverging channel defined by the secondary flaps. The primary and secondary flaps are conventionally movable between a generally closed position having a minimum throat area and a minimum outlet area at the aft end of the secondary flaps, and to a generally fully open position having a maximum throat area and a maximum outlet area.
Such converging-diverging (C-D) exhaust nozzles may either be axisymmetric or two-dimensional, or rectangular. In a two-dimensional C-D nozzle, the primary and secondary flaps extend transversely between a pair of spaced, nozzle sidewalls which collectively bound the exhaust gases being channeled therethrough. Since the primary and secondary flaps move relative to the stationary sidewalls, suitable seals are typically provided therebetween for reducing, if not eliminating, leakage of the exhaust gases from the converging and diverging channels, between the flaps and the sidewall, and outwardly therefrom. Leakage of the hot exhaust gases would require suitable thermal protection of components adjacent to the exhaust nozzle including, for example, hydraulic and electrical systems. Leakage of the exhaust gases also decreases the propulsion efficiency of the exhaust nozzle.
During operation of the exhaust nozzle, the gap between the exhaust flap and the nozzle sidewalls may expand due to pressure loading by the exhaust gases up to about 2.5 cm, for example. A suitable seal, therefore, must be able to bridge this relatively large gap while maintaining effective sealing, and should be relatively small for minimizing the use of space in the exhaust flap. Furthermore, since the seals are subject to hot exhaust gases, they must be effective for withstanding such temperatures for obtaining useful lifetimes.
For example, one type of conventional seal for an exhaust nozzle includes a hinged leaf seal effective for bridging a large gap between the exhaust flap and the sidewall. However, exhaust gas leakage through the hinge thereof decreases nozzle aerodynamic performance. Minimizing or reducing the amount of such hinge leakage has conventionally resulted in a more complex leaf seal.